People are generally aware of the most common causes of hallucinations, like schizophrenia and a really high fever. But lesser known are the more rare causes; here are six you probably haven't heard about.

Brace yourselves: the deadly hemorrhagic fever, Ebola, seems to be transmissible between species. In addition, the same study finds that pigs could be an unlikely source for passing on the disease.

Ebola has been found in gorillas, chimps, small antelopes called duikers, and of course humans, according to The Scientist Magazine. Up until 2009, researchers were not even aware that pigs could carry Ebola. After all, though Ebola appears to be native to the continent of Africa, pigs are relatively new to the land mass.

Researchers found that pigs carried a strain of Ebola in 2009, though they did not appear to show symptoms. Although the strain carried by pigs, Reston Ebola, has not appeared to be harmful in humans yet, though pig farmers had antibodies in their immune systems.

More troublingly, pigs can be infected with the Zaire-Ebola virus. That strain can be passed between pigs through direct contact. The Zaire-Ebola virus is the deadliest form of the disease, and has killed 90 percent of the people infected with it.

In a study published in Scientific Reports, researchers infected pigs with the Zaire-Ebola virus. They were placed in the same room as macaque monkeys, though the two species did not touch because there was a barrier placed between them. Within two weeks, the pigs had passed on the infection to macaques.

The pigs breathed more heavily and had fevers, but they were otherwise all right. The macaques were not so fortunate. The primates developed bloody spots on their chests and limbs, and their lungs appeared to be damaged.

Researchers remain unsure whether the virus is airborne though. They believe that it is possible that the virus had spread through respiratory droplets, like from sneezing, when they were cleaning the pigs' cages. Outbreaks do not indicate that the virus is particularly effective if it is airborne.

However, if the virus is not airborne, it does raise the question of how some of the farmers had antibodies of the Reston Ebola virus, when they had never come into contact with infected tissue. Researchers also note that, of the 2,200 cases of Ebola since the virus's discovery in 1976, only 13 have occurred because of direct contact with an infected person, animal, or their body fluid.

Three deaths from Ebola have cropped up in Uganda recently, just months after the country finished battling a previous outbreak of the disease.

Researchers had previously thought that Ebola, a disease that can have symptoms as subtle as fatigue and as horrifying as internal bleeding, was transmitted through contact with bodily fluids. This study puts that idea into question, and makes a scary disease even scarier.